A usual timepiece anti-shock device includes a resilient member which bears on or which exerts a pressure against at least one endstone of the bearing comprising the anti-shock device, the endstone forming a stop for the pivot inserted into the bearing in the direction of the axis of rotation of the pivoting element concerned. This anti-shock device is arranged to be able to generate, through the endstone, a restoring force on the pivot in question, when the pivot presses against the endstone in the event of a shock. It is understood that “endstone” means any structure, made of any suitable material, which defines an axial bearing surface for the pivot.
Such anti-shock devices generally include mechanical springs which are dimensioned empirically, according to practical rules, such as that of the best compromise between mechanical stability in operation and elastic resistance to mechanical deformations. Indeed, it is desirable to have a relatively stiff shock absorber which does not cause axial movements of the pivoting element with each small shock, while ensuring the shock absorber function for violent shocks causing high axial (positive or negative) accelerations for the pivoting element which could damage its pivots.
In particular, conventional anti-shock devices for the sprung balance, “parachutes” and lyre-springs, are dimensioned such that they are only actuated upon relatively high shock accelerations (between 200 g and 500 g, g being the earth's acceleration), as a result of the prestress of the spring forming these “parachutes” and lyre-springs, which defines a threshold value. Beyond this threshold value, it is provided that the spring deforms and absorbs part of the shock energy. However, because of the low mechanical shock absorption of the metallic strips used, most of the energy is restored to the balance. Local deformation of the balance pivot is thus highly probable, even for relatively low shocks. Such a deformation, which has a considerable impact on the chronometric precision of the watch, is generally ignored because the certified chronometer standard for the chronometric stability of a watch following a one meter shock is not strict (difference of 60 seconds/day).